WEDNESDAY, Dec. 18, 2013 (HealthDay News) -- Despite some concerns to the contrary, children whose moms used antidepressants during pregnancy do not appear to be at increased risk of autism, a large new Danish study suggests.

The results, published Dec. 19 in the New England Journal of Medicine, offer some reassurance, experts said.

There have been some hints that antidepressants called selective serotonin reuptake inhibitors (SSRIs) could be linked to autism. SSRIs are the "first-line" drug against depression, and include medications such as fluoxetine (Prozac), sertraline (Zoloft), citalopram (Celexa) and paroxetine (Paxil).

In one recent U.S. study, mothers' SSRI use during pregnancy was tied to a twofold increase in the odds that her child would have autism. A Swedish study saw a similar pattern, though the risk linked to the drugs was smaller.

But both studies included only small numbers of children who had autism and were exposed to antidepressants in the womb.

The new study is "the largest to date" to look at the issue, using records for more than 600,000 children born in Denmark, said lead researcher Anders Hviid, of the Statens Serum Institute in Copenhagen.

And overall, his team found, there was no clear link between SSRI use during pregnancy and children's autism risk.

Hviid cautioned that the finding is still based on a small number of children who had autism and prenatal exposure to an SSRI -- 52, to be exact. The researchers noted that it's not possible to rule out a small increase in autism risk.

But, Hviid said, "at this point, I do not think this potential association should feature prominently when evaluating the risks and benefits of SSRI use in pregnancy."

Commenting on the findings, Christina Chambers, director of the Center for the Promotion of Maternal Health and Infant Development at the University of California, San Diego, stated, "I think this study is reassuring."

One "important" point, Chambers added, is that the researchers factored in mothers' mental health diagnoses -- which ranged from depression to eating disorders to schizophrenia.

"How much of the risk is related to the medication, and how much is related to the underlying condition?" Chambers said. "It's hard to tease out."

In theory, she noted, depression or other mental health disorders could contribute to autism risk because those moms may be more likely to make unhealthy lifestyle choices, such as smoking or drinking.

In this study, Hviid's team did initially see a slightly increased risk of autism among children whose mothers used SSRIs during pregnancy. But once the researchers factored in the psychiatric disorders themselves, that statistical link fell away.

On top of that, there was a slight increase in autism risk among children whose mothers had used an SSRI in the two years before pregnancy, but not during pregnancy.

Hviid said that all suggests it's the underlying conditions, rather than the drugs, that are associated with a small autism risk -- though the reasons, he added, are unknown.

The study, which was funded by the Danish government, is based on records from Denmark's national system of health databases. Of nearly 627,000 children born between 1996 and 2005, just under 3,900 were later diagnosed with autism.

Among those children, 52 were born to mothers who filled an SSRI prescription during pregnancy. There were just over 6,000 other children whose mothers used the antidepressants during pregnancy but did not develop autism.

Both Hviid and Chambers said the findings do not prove that SSRIs carry no autism risk. And a connection is biologically plausible, Hviid said.

No one knows what causes autism, which affects an estimated one in 88 children. But it involves a disruption in fetal brain development. It's thought that serotonin -- the chemical that SSRIs target -- contributes to early brain development, and in animals, altered serotonin levels can affect brain function and behavior.

"It's still worthwhile to continue to study this," Chambers said.

But, she added, based on the human studies so far, "if there is any increased risk of autism, it appears small."

And for any one woman, Chambers said, that possible risk would have to be balanced against the risks of leaving major depression untreated.

"For some women, the optimal situation may be to take an SSRI, even if there is an association [with autism]," Chambers said.

Hviid agreed, saying that's a decision that has to be left up to women and their health care provider.